This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-263665, filed Sep. 17, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a photolithography technology for manufacturing a semiconductor device, and more particularly to a method for manufacturing an exposure mask in which a pattern arrangement on the mask is designed, and an exposure apparatus using the mask, and furthermore a method for manufacturing a semiconductor device.
In recent years, in the field of the manufacture of semiconductors, an exposure apparatus is widely used for transcribing, in a reduced manner on a resist on a wafer, an LSI pattern formed on a reticules (an exposure mask) in order to form a fine pattern on the wafer.
When an optical system is ideal in this kind of exposure apparatus, the same optical contrast, the resist pattern and the exposure margin can be obtained in the repeated patterns with several xcexcm or more. However, actually, there arises a phenomenon in that the resist pattern and the exposure margin differ depending upon the mask open ratio of the used reticule. Specifically, in the case where the positive type resist is used, the exposure margin is narrowed both exposure latitude and Depth of Focus (DOF) with an increase in the mask open ratio of the reticule with the result that a decrease in the resist pattern becomes drastic. This phenomenon is conspicuous particularly in a fine pattern in the vicinity of the resolution limit.
Furthermore, in the case where the mask open ratio is locally different even on the same reticule as well, for example, a line and space (L/S) pattern formed of Cr on the circumference of tens of xcexcm and the resist pattern profile on the wafer corresponding to the L/S pattern all formed of glass on the circumference of tens of xcexcm differ from each other. It is considered that these phenomena results from the fact that the stray light which is not generated in an ideal exposure apparatus is irradiated as a background light on the wafer depending on the mask open ratio, so that the optical contrast is lowered.
In the case where the mask open ratio of the reticules differs, it is sometimes difficult to apply the same resist process in the same object pattern because of the above phenomenon. A huge amount of labor and cost is required to construct a resist process depending on the mask open ratio of the reticule of each layer in order to solve this problem. Furthermore, in the case of system on chip (SOC), that consists of memory portion and logic portion, there arises a case in which an exposure margin/resist pattern profile of a small-scale cell for a cache in the logic portion having a high mask open ratio, a large-scale cell of a memory portion having a low mask open ratio largely differs in some cases.
In this manner, in the exposure apparatus for photolithography which can be currently used, the light intensity contrast of the transcribed pattern is lowered because of the presence of the background light rather than an ideal value calculated from the illumination condition. As a consequence, there is a problem that the exposure margin is narrowed, and the resist profile is poored. Furthermore, the reduction of the light intensity contrast becomes conspicuous with an increase in the mask open ratio.
An object of the present invention is to provide an exposure mask which lowers the intensity of the background light and which can suppress the lowering of the light intensity contrast of the transcribed pattern, an exposure apparatus, and a method for manufacturing a semiconductor device.
The exposure mask can be used to transcribe a desired pattern on a resist on a wafer in the photolithography step. This exposure mask is formed by the arrangement of the transcribed pattern film formed on a desired pattern on a transparent substrate. In the present invention, the intensity of the background light is decreased. In order to suppress the lowering of the light intensity contrast of a desired pattern, a dummy pattern film formed in a dummy pattern is arranged on a transparent substrate together with the transcribed pattern film. The dummy pattern is designed in such a manner that the dummy pattern is not transcribed under an exposure condition which is required for transcribing the desired pattern on a resist in a desired size. Besides, the dummy pattern film is arranged from the transcribed pattern film in a predetermined distance in such a manner that the intensity distribution of light which passes through the transcribed pattern film is not deformed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.